480 FXUS66 KPQR 241614 AFDPQR Area Forecast Discussion...corrected National Weather Service Portland OR 910 AM PDT Mon Apr 24 2017 .SYNOPSIS...Expect periods of rain through midweek with decreasing showers Thursday and Friday. Drier weather looks to return Saturday, but is looking short lived with additional wet weather possible Sunday and Monday. && .SHORT TERM...Today through Thursday...Water vapor satellite imagery reveals an upper level trough sagging southeastward across the Pacific Northwest. A pocket of -28 to -30C 500mb temperatures is currently off the Washington coast and will drop southeastward across the area this afternoon. Closer to the ground, a surface low pressure is currently moving onto the Oregon coast and will push eastward towards the PDX metro and Columbia River Gorge today. The net effect will be the widespread rain and mountain snow this morning transitioning to a showery pattern this afternoon. Will leave a thunder mention out of the forecast for now as it looks marginal this afternoon, but will monitor trends and update the forecast accordingly if it looks like we will get sufficient surface heating. In addition, areas to the south of the low pressure track will see gusty southerly winds increase later this morning and early this afternoon...likely into the 25-35 mph range for a couple hours. Shortwave ridging building into the Pacific Northwest should bring a fairly quick decrease in showers tonight. However, the next occluding frontal storm system will push more rain towards the area Tuesday. The 12z GFS sped up precipitation timing closer to the 00z EC solution and suspect most of the region will be wet by at least late Tuesday afternoon...if not sooner. A 150-160kt jet will then take aim at Oregon Tuesday night with our CWA generally on the polar side of the jet through Thursday. This should produce plenty of showers with lowering snow levels across the Cascades. Additional Winter Wx highlights for the Cascades look possible. /Neuman .LONG TERM...No Changes. Previous discussion follows...Wednesday night through Sunday...Showers will continue across the forecast area Wednesday night into Friday as a couple of more disturbances ride through on a jet stream that turns more northwesterly through through Friday. The models are now in better agreement that enough of an upper ridge will build early in the weekend for some drying. The next system is expected about Sunday. Tolleson && .AVIATION...Surface low moving onshore around KTMK has weakened somewhat. However, still expect probable gusts 20-25 kt south of a KTMK to KUAO line through roughly 23z. Coastal areas are expected to remain predominantly MVFR in cigs and vis with pockets of IFR Vsbys as the low moves ashore. Most guidance holds MVFR at the coast through at least 06Z Tue, but there is some chances for improvement after that. Inland, MVFR Cigs and Vsbys have become more dominant and should last through 22-00Z with trends toward VFR after that. Precipitation becomes showers after midday as the low/front shifts east of the area. Could then see some heavier showers and cumulus buildups for the remainder of daylight hours today as the lower level instability could favor fairly deep cell growth. Showers quickly taper off later this evening. Forecast guidance has coastal terminals remaining MVFR through the night with inland terminals picking up an MVFR Cig 020-030 after 25/12z and lasting until at least 25/18z. KPDX AND APPROACHES...MVFR conditions primarily from cigs around 025 and occasional Vsbys are expected through midday. Cigs should then begin to break and lift, however, heavier showers could briefly bring MVFR cigs and vis this afternoon into early evening. /JBonk && .MARINE...Surface low has moved onshore in the general vicinity f Tillamook during the past hour. Have already begun to see wind shifts to the west south of the low. Areas north of the low will see a more dramatic wind shift from south to southeast to northwest by afternoon. Lower end SCA wind gusts 20-25 kt will continue this afternoon. A minor dynamic fetch has brought seas 10-12 ft mainly south of the low as well. Should see the seas subside shortly after the winds diminish this afternoon. Active weather pattern continues as there is another system on Tuesday that will likely bring high-end small craft advisory wind and possibly brief low-end gales. Seas look to remain around 7 to 9 ft. Surface high pressure then begins to build offshore shunting the surface lows mainly north of the waters and keeping a relative lull in winds through Friday. Seas next reach 10-11 ft Thursday through early Friday as the southern end of a swell train clips the northern waters from a surface low crossing the Alaskan Panhandle. /JBonk && .PQR WATCHES/WARNINGS/ADVISORIES... OR...Winter Weather Advisory until 8 PM PDT this evening for Cascades in Lane County-Northern Oregon Cascades. WA...Winter Weather Advisory until 8 PM PDT this evening for South Washington Cascades. PZ...Small Craft Advisory for winds until 2 PM PDT this afternoon for Coastal Waters from Cape Shoalwater WA to Cascade Head OR out 60 nm. Small Craft Advisory for winds until 4 PM PDT this afternoon for Coastal Waters from Cascade Head OR to Florence OR out 60 nm. Small Craft Advisory for hazardous seas until 5 PM PDT this afternoon for Coastal Waters from Cascade Head OR to Florence OR out 60 nm. Small Craft Advisory for Rough Columbia River Bar from 2 PM this afternoon to 6 PM PDT this evening. Small Craft Advisory for Rough Columbia River Bar from 3 AM to 7 AM PDT Tuesday. && $$ Interact with us via social media: www.facebook.com/NWSPortland www.twitter.com/NWSPortland This discussion is for Northwest Oregon and Southwest Washington from the Cascade crest to 60 nautical miles offshore. The area is commonly referred to as the forecast area.
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